C1 Atomic Structure

• The nucleus contains protons and neutrons. It has a positive charge because of the protons. Almost the whole mass of the atom is concentrated in the nucleus.
• Electrons move around the nucleus in electron shells. They are negatively charged and small. The volume of the orbits determine the size of the atom .
• The relative mass of a proton is 1. The relative charge is +1.
• The relative mass of a neutron is 1 and the relative charge is 0.
• The relative mass of an electron is very small and the relative charge is -1.
• The atomic number is the number of protons in an atom of an element.
• An atom has an overall charge of 0, so the number of protons is the same as the number of electrons.
• The mass number is the total number of protons and neutrons in an atom. To get the number of neutrons subtract the atomic number from the mass number.
• An isotope is the same number of protons but different number of neutrons.
• The relative atomic mass is an average mass taking the different masses and abundances (amounts) of the isotopes that make up the element.
• An element is a substance only containing atoms with the same number of protons.
• relative atomic mass: the sum of (isotope amount x isotope mass number) / sum of amounts in all isotopes.
• Compounds are formed by chemical reactions. Chemical reactions involve the formation of one or more new substances often involve an energy change.
• Compounds contain two or more elements chemically combined in fixed proportions held together by chemical bonds. Making bonds involves atoms giving away, taking or sharing electrons.
• Compounds can only be separated into elements by chemical reactions.
• Ionic bonds are between metals and non metals. Metals lose electrons to form positive ions and non-metals gain electrons to form negative ions.
• Covalent bonding: Compounds formed from non-metals consists of molecules. Each atom shares an electron with another atom.
• Metallic bonding: Occurs in metallic elements and alloys.
• Balanced equations must have the same number of atoms on both sides.
• A mixture consists of two or more elements or compounds that are not chemically combined together. The chemical properties of each substance in the mixture is uncharged.
• The parts of a mixture can either be elements or compounds. The chemical properties of a substance aren't affected by it being a part of a mixture.
• In an electron shell, the lowest energy levels are always filled first because they're closest to the nucleus.
• In a nucleus the electron wants to gain a full outer shell.
• The order of an electron shell is 2,8,8
• Before the discovery of protons, neutrons and electrons, scientists attempted to classify the elements by arranging them in order of their atomic mass and their physical and chemical properties.
• The early periodic tables were incomplete and some elements were placed in inappropriate groups of atomic weights.
• Elements with properties predicted by Mendeleev were discovered and filled the gaps. Knowledge of isotopes made it possible to explain why the order based on atomic weights was not always correct.
• In the periodic table elements are laid out in order of increasing atomic (proton) number. This means the properties of elements are similar.
• Metals are on the left and non-metals are on the right of the periodic table.
• Elements with similar properties form colums.
• The vertical columns are called groups.
• The rows are called periods.
• The group number tells you how many electrons are in the outer most shell. The exception is group 0.
• Elements that react to form positive ions are metals. The majority of elements are metals.
• Metals are found to the bottom and to the left of the periodic table.
• All metals have metallic bonding.
• The properties of metals:

  • Strong and malleable
  • Great at conducting heat and electricity
  • Contain high boiling and melting points
• • Metals to the left of the periodic table don't have many electrons to remove. Metals towards the bottom of the periodic table have outer electrons far away from the nucleus so many have a weaker attraction. Not much energy is needed to remove the electrons so it is easy for the elements to react to form positive ions with a full outer shell.
• Non-Metals forming positive ions is more difficult. They contain lots of electrons to remove. At the top of the periodic table the outer electrons are close to the nucleus so feel a strong attraction. It's easier for them to share or gain electrons to get a full outer shell.
• Properties of non-metals:

  • dull
  • brittle
  • aren't always solids
  • don't generally conduct electricity
  • contain a low density